ES2335574T3 - METHOD FOR PRODUCING A BIAXIALALLY STRETCHED CELL MADE FROM VINYL ETHYLENE-ALCOHOL COPOLYMER. - Google Patents

Abstract

A method of producing a biaxially stretched film comprising: stretching a film made primarily of an ethylene-vinyl alcohol copolymer having an ethylene content of 15 to 70 mol% and a saponification degree of 80 mol% or more, under heating, cooling the film, and subjecting the cooled film to a heat treatment, in which the heating temperature during stretching is 60 to 160 ° C, the cooling temperature is a temperature of 30 to 100 ° C lower than the temperature of heating during stretching, and the temperature for heat treatment is 150 to 190 ° C.

Description

Method to produce a biaxially film stretched made of ethylene-alcohol copolymer Vinyl

The present invention relates to a method to produce a biaxially stretched film made of copolymer  ethylene-vinyl alcohol (referred to here as forward "EVOH") which has a small coefficient of thermal contraction, a small coefficient of curvature and excellent shape stability. The present invention relates also to a biaxially stretched film obtained by this method and a stratified one that includes this movie.

The document US-A-4124677 describes a method for make a biaxially polyvinyl alcohol film stretched out

EVOH biaxially stretched films are they use a lot as a material that has excellent properties of gas barrier A stratified that is obtained by stratifying the biaxially stretched EVOH film and a resin film thermoplastic that has excellent moisture resistance and mechanical properties, especially a resin film of Polyolefin, is used as multilayer plastic packaging material in Several fields For example, such a laminate is widely used as vessel that has excellent oxygen barrier properties in the form of bags, tubes, cups and sachets in various fields such such as food, cosmetics, pharmaceuticals, chemicals and doctors, and bath products. In recent years, the vessels for food, in particular, they have become more often heated for sterilization before or after filling with foods. Therefore, a material is demanded that has not only excellent oxygen barrier properties but also a Small coefficient of thermal shrinkage in dry.

According to the present invention it has been found that when a biaxially stretched EVOH film is selected that It has a small dry thermal shrinkage coefficient, and it stratify on it a polyofefin film as described previously, then the stratified one is likely to be wavy obliquely (henceforth, this undulation is called "S-shaped ripple") with respect to the longitudinal direction (machine direction; MD). Also, according to the present invention has been found that when larger the ripple coefficient of the EVOH film is more likely than an S-shaped ripple occurs. In the stretched film, considering the general knowledge that thermal contraction dry and ripple are contradictory properties, it seemed difficult to control both properties at the same time.

However, according to the present invention it has been found that when an EVOH is used that has a composition specific and specific production conditions are selected, Dry thermal shrinkage and film ripple biaxially stretched EVOH can be suppressed weather.

A method according to claim 1 for produce a biaxially stretched film of the present invention  comprises: stretching a film made primarily of a ethylene-vinyl alcohol copolymer having a ethylene content of 15 to 70 mol% and a degree of saponification of 80 mol% or more with heating; cool the movie; and subject the cooled film to a heat treatment; in which a heating temperature during stretching is from 60 to 160 ° C, a cooling temperature is a temperature  30 to 100 ° C lower than the heating temperature during the stretching, and a temperature for heat treatment is from 150 to 190 ° C.

In a preferred embodiment, the stretching is simultaneous biaxial stretching.

In a preferred embodiment, a preheating from 60 to 160ºC before stretching.

In a preferred embodiment, a ratio of stretching in a longitudinal direction is 2.5 to 4.5, a Stretch ratio in a transverse direction is 2.5 to 4.5, and an area stretch ratio is 7 to 15 in the biaxially stretched film.

In a preferred embodiment, a coefficient of Ripple of the biaxially stretched film is 15% or less.

A biaxially stretched copolymer film ethylene-vinyl alcohol of the present invention It is described in claim 6.

A laminate of the present invention it comprises a layer made of the biaxially stretched film of ethylene-vinyl alcohol copolymer and one layer Made of another thermoplastic resin.

In a preferred embodiment, the resin Thermoplastic is a polyolefin.

Thus, the present invention described here it makes possible the advantages of providing a method for produce a biaxially stretched EVOH film in a way stable and in massive quantities, in which the film has a small coefficient of dry thermal shrinkage, a small ripple coefficient, and excellent properties such as shape stability; providing a biaxially film stretched obtained by the method that has a high utility for packing; and providing a laminate that includes a layer made of biaxially stretched film and a layer made of another thermoplastic resin that is in contact with the previous layer, and It is properly used as packaging material.

Figure 1 is a schematic view for illustrate the generation of undulation in a stretching procedure Biaxially an unstretched film.

Figures 2A and 2B are schematic views that show a change in the size of a circular cut film in a dry thermal shrinkage test of the film stretched out

In the present invention, EVOH, which is a Raw material for biaxially stretched film can be produce saponifying a copolymer containing ethylene and a vinyl ester as main components with, for example, a alkaline catalyst Examples of the vinyl ester include a fatty acid vinyl ester, and one of its typical examples is vinyl acetate You can exemplify others other than this, vinyl propionate, vinyl pivalate or the like.

The ethylene content of EVOH must be 15 at 70 mol%, preferably 20 to 50 mol%, and more preferably 25 to 45 mol%. When the ethylene content is less than 15 mol%, the gas barrier properties in high humidity of the film obtained are reduced and the melt moldability. When it exceeds 70 mol%, it is not they can obtain sufficient gas barrier properties.

This EVOH may contain a small amount of another monomer as a copolymer component (a copolymer unit),  as long as it does not interfere with the advantages of this invention.

The amount of the monomer (that is, units of monomer other than ethylene units and units of vinyl alcohol) contained in the EVOH is 10 mol% or less, preferably 5% by mole or less, and more preferably 2% by moles or less based on the total moles of monomers that form the EVOH

Examples of monomer that can be polymerize include α-olefins such as propylene, 1-butene, isobutene, 4-methyl-1-pentene, 1-hexene, and 1-octene; acids unsaturated carboxylic acids such as itaconic acid, acid methacrylic, acrylic acid, maleic anhydride, its salts, its partial or complete esters, their nitriles, their amides, and their anhydrides; vinyl silane compounds such as vinyltrimethoxysilane; unsaturated sulfonic acids or their salts; alkylthioles; and vinyl pyrrolidones.

The degree of saponification of the component of EVOH vinyl ester must be 80 mol% or more, preferably 90 mol% or more, more preferably 95% mol moles or more, and even more preferably 98% moles or more. When the degree of saponification is less than 80 mol%, it reduce the high humidity gas barrier properties of the film that includes this EVOH, and also deteriorates the thermal stability of EVOH. Therefore, it is likely to be produce gels or aggregates in the film.

Two or more types of EVOH can be mixed to its use as EVOH. In this case, the average value is determined obtained based on ethylene content or the degree of saponification of each EVOH in view of the weight ratio of the mixture as the ethylene content or degree of saponification of the EVOH In addition, when a film is formed with EVOH, you can mix a resin (polyamide, polyolefin, etc.) other than EVOH, additives and the like as long as it does not practically interfere with The objective of the present invention.

Usually, the amount of resin that is you can mix with EVOH is 50 parts by weight or less, preferably 10 parts by weight or less, more preferably 5 parts by weight or less and most preferably 2 parts by weight or less based on 100 parts by weight of EVOH. The amount of additives that can be mixed with EVOH is 30 parts by weight or less, preferably 10 parts by weight or less, more preferably 5 parts by weight or less and most preferably 2 parts by weight or less based on 100 parts by weight of EVOH.

Examples of additives include a thermal stabilizer, an ultraviolet absorber, an antioxidant, a coloring agent and a filler. The melting point of the EVOH is preferably in the range of 140 to 220 ° C.

To produce a biaxially stretched film by the present invention, first, a film is produced without stretch by the use of EVOH described above alone or by use EVOH to which other resin and / or additives are added if necessary. There is no particular limitation with respect to the method of producing the unstretched film. For example, the unstretched film can be produce by an EVOH melt extrusion process using a screw extruder that has a nozzle T for the film formation, and then cool the film formed. The film forming temperature is preferably in the range of 200 to 280 ° C. When the film forming temperature is less than 200 ° C, the EVOH melt flow is insufficient, and therefore it It can impair the ability of film formation. When the film forming temperature exceeds 280 ° C, the EVOH it can be decomposed by heat and the resulting film can be colored

The temperature to cool the film without stretch described above is preferably in the range from 0 to 40 ° C. If a cooling temperature of less is used at 0 ° C, special equipment is required, which is disadvantageous because of the cost. When the cooling temperature is used that exceeds 40 ° C, a prolonged cooling period is required, so It reduces productivity.

The thickness of the unstretched film of EVOH obtained in this way is preferably 100 to 300 µm in view of the handling properties in the procedure of stretching.

The biaxially stretched film of the present invention can be obtained by a procedure that includes stretching the unstretched film with heating, cool the film, and subject the film to a heat treatment. The temperature of heating to stretch the film is 60 to 160 ° C. The cooling temperature is a temperature of 30 to 100 ° C more lower than the heating temperature to stretch the film, and  The temperature for the heat treatment is 150 to 190 ° C.

When the film is biaxially produced drawn from EVOH by the procedure described above, it is preferably allow the unstretched film to contain moisture for production stability. The moisture content of the film is preferably 1 to 30% by weight, more preferably from 1 to 20% by weight. When the moisture content of the film It is less than 1% by weight, the film is likely to break in the stretching procedure When it exceeds 30% by weight, the Mechanical strength of the biaxially stretched film tends to be insufficient

It is preferable to preheat prior to stretching the film with heating to Stability production The temperature for Preheating is preferably 60 to 160 ° C, and more preferably from 70 to 140 ° C. It is preferable to determine the preheating temperature considering the temperature of heating to stretch the film. More specifically, the preheating temperature is preferably in the range within ± 20 ° C of the heating temperature To stretch the movie. The preheat period is preferably in the range of 2 to 30 seconds, more preferably in the interval of 3 to 10 seconds.

As described above, the temperature heating to stretch the film should be 60 to 160 ° C, and preferably from 70 to 140 ° C. When the temperature of heating to stretch the film is less than 60 ° C, the coefficient of curvature of the biaxially stretched film obtained is large, so it is very possible that a S-shaped ripple in a laminate that includes the film biaxially stretched finally obtained. When it exceeds 160 ° C, The mechanical strength of the biaxially stretched film is insufficient. The stretch period of the film under heating is preferably in the range of 2 to 30 seconds, more preferably in the range of 3 to 10 seconds.

As biaxial stretching, the simultaneous biaxial stretching or biaxial stretching sequential. Among them, biaxial stretching is preferable simultaneous with respect to productivity. The relationship of stretching is preferably 2.5 to 4.5 in the direction longitudinal (machine direction; MD), and preferably of 2.5 to 4.5 in the transverse direction (width) (TD), and the ratio Area stretching is preferably 7 to 15. The ratio Stretching is more preferably 2.5 to 3.5 in the direction longitudinal, and 2.5 to 3.5 in the transverse direction; and the area stretch ratio is more preferably 8 to 12.

The movie that has been stretched biaxially from The manner described above is cooled below. The cooling temperature should be 30 to 100 ° C lower than the heating temperature to stretch the film, and preferably from 35 to 75 ° C lower than the temperature of heating. The cooling temperature is generally 0 at 80 ° C, and preferably from 40 to 75 ° C. When the difference between The heating temperature and the cooling temperature is less than 30 ° C, the coefficient of curvature of the film biaxially stretched obtained is large, so it is very possible that an S-shaped ripple occurs in a laminate that It includes the biaxially stretched film finally obtained. When the difference between the heating temperature stops stretch the film and the cooling temperature exceeds 100 ° C, the coefficient of thermal dry shrinkage of the film Biaxially stretched obtained is large. The period of cooling is preferably 3 to 10 seconds.

The temperature for heat treatment after cooling it should be 150 to 190 ° C, and preferably from 155 to 185 ° C. When the temperature for heat treatment is less than 150ºC, stretching relaxation is insufficient, of so that the stability of film size deteriorates biaxially stretched obtained. When it exceeds 190 ° C, the coefficient of curvature is large, so it is very possible that an S-shaped ripple occurs in a laminate that includes the biaxially stretched film obtained (especially, a laminate that includes a polyolefin layer). The period of heat treatment is preferably 2 to 30 seconds, and more preferably from 2 to 20 seconds.

The coefficient of curvature of the film biaxially stretched EVOH obtained by the method above described is preferably 15% or less and more preferably 12% or less. When the curvature coefficient exceeds 15%, it is very an S-shaped ripple may occur in a laminate which includes the biaxially stretched film obtained and is deteriorate form stability in its use. In memory of descriptive, the "curvature coefficient" is a value defined as follows.

Figure 1 shows a schematic view that shows a procedure in which a long unstretched film It stretches continuously under heating. A line 2 is drawn straight on a portion 1 without stretching a film in the direction transverse of the film. When the film is stretched under heating (stretching particularly in the direction of the width) while moving the film in the longitudinal direction,  the central portion in the direction of the film width it is usually delayed in movement, compared to portions near both edges of the film. Therefore, the Straight line 2 becomes an arc-shaped curve line 21. The value obtained from the following equation is called the coefficient BW curvature (%).

BW = (a / b) x 100, where a is the maximum delay distance on line 21 curve, and b is the width of the biaxially stretched film.

The dry thermal contraction coefficient in the longitudinal direction (MD) of the biaxially stretched film of EVOH obtained by the method described above is preferably 4.0% or less, and more preferably 3.5% or less. When the coefficient of dry thermal shrinkage in the direction Longitudinal (MD) exceeds 4.0%, the size stability of the film deteriorates. Here, the "contraction coefficient thermal thermal in the longitudinal direction (MD) "refers to a contraction coefficient in the longitudinal direction when a biaxially stretched film of EVOH is subjected to treatment Dry thermal (i.e. the film heats up without supplying additional humidity) at 140 ° C for one hour. The thickness of the biaxially stretched film of EVOH obtained is generally of 5 µm to 30 µm, depending on the application of the movie.

It is possible to control both the contraction Dry thermal as the curvature using the method of the present  invention as described above. In general, the Dry thermal shrinkage coefficient becomes small performing heat treatment sufficiently after stretching, but in this case, the coefficient of curvature tends To be big. As a result of the inventors' investigation of the present invention, the cooling process to a default temperature is performed between the procedure of stretching done at a predetermined temperature and the heat treatment procedure that is performed at a predetermined temperature, so that the increase in coefficient of curvature can be advantageously suppressed.

EVOH's biaxially stretched film obtained in this way can be used alone or can be used in the form  of a laminate that includes a layer made of the film biaxially stretched and a layer made of another resin thermoplastic Examples of the thermoplastic resin include polyolefin (for example, polyethylene, polypropylene, poly (1-butene), poly (4-methyl-1-pentene), an ethylene-propylene copolymer, a copolymer of ethylene and? -olefin which has at least 4 carbon atoms, a copolymer of polyolefin and anhydride maleic, an ethylene-vinyl acetate copolymer, an ethylene acrylate copolymer, and a polyolefin  modified obtained by graft modification of any one of these compounds with an unsaturated carboxylic acid or with one of its derivatives), nylon (for example, Nylon 6, Nylon 66, copolymer Nylon 6/66), polyvinyl chloride, polyurethanes, polyacetals, and poly (alcohol resins) vinyl) modified.

There is no particular limitation with respect to the stratified structure. The structure examples include XY, YXY, XYZ, and the like in which X is the movie biaxially stretched EVOH and Y and Z are other layers of resin thermoplastic There is no particular limitation regarding the method Stratification For example, methods can be commonly used used in this field such as extrusion stratification, dry stratification, and solution coating.

The biaxially stretched EVOH film of the present invention and the laminate that includes the film biaxially stretched EVOH have excellent properties of gas barrier, shape stability, and transparency, so which can be used primarily as packaging material for foods.

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Examples

Later, the present invention will be will describe more specifically by way of examples, but the The present invention is not limited to them. In the examples, the Movies were evaluated as follows.

(1) Dry thermal shrinkage coefficient of film in the longitudinal direction

A circular film 3 with a diameter of 10 cm as shown in Figure 2A is cut from the central portion in the width direction (TD) of a biaxially long film stretched out This film is subjected to a dry heat treatment at 140 ° C for one hour and then cooled to temperature ambient. The length L (cm) in the longitudinal direction (is say, MD of the biaxially stretched long film) of the treated film 3 (see Fig. 2B) is read by vernier calipers, and the coefficient S (%) of dry thermal shrinkage in the direction Longitudinal (MD) is obtained with the following equation.

S = {(10-L) / 10} x 100

(2) Coefficient of curvature

As shown in Figure 1, a drawing is drawn straight line 2 with an oil ink in the width direction of a long film without stretching. The film heats up while it moves in the longitudinal direction for biaxial stretching. In this stretching procedure, since the central portion of the film is delayed in the direction of movement, the stretching is not uniform so that straight line 2 is turns an arc-shaped curve line 21. The value obtained of the following equation is called the BW curvature coefficient (%)

BW = (a / b) x 100, where a is the distance maximum delay in line 21 curve, and b is the width of the biaxially stretched film.

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Example 1

An EVOH resin that has a content of 32 mol% ethylene, a 99.5% saponification grade and a melting point of 183 ° C was melted at 230 ° C and extruded into a T nozzle on a molding roller that has a surface cooled to 15 ° C. At the time of extrusion, the film of extruded resin was blown with air from an air knife to a air flow of 30 m / s. In this way, a film was obtained without stretch that is 150 µm thick. This movie was submerged in hot water at 50 ° C for about 15 seconds. He Moisture content after immersion was 3.0% by weight. Using a simultaneous biaxial stretching machine, the film was preheated at 140 ° C for 8 seconds, stretched up to three times its size in each of the longitudinal and transverse directions at 140 ° C, and then cooled to 70 ° C for 7 seconds, followed by a heat treatment at 175 ° C for 3 seconds. From In this way, a biaxially stretched EVOH film was obtained. The Table 1 shows the dry thermal contraction coefficient and the coefficient of curvature of this film. Table 1 also shows the results of Examples 2 to 4 and the Examples Comparatives 1 to 3, which will be described below.

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Examples 2 a 4

Biaxially stretched films were obtained EVOH in the same manner as in Example 1 except that the preheating temperature, stretching temperature, stretch ratio, cooling temperature, heat treatment temperature and moisture content of the unstretched film were changed to those shown in the Table one.

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Comparative Examples 1 to 3

Biaxially stretched films were obtained EVOH in the same manner as in Example 1 except that the preheating temperature, stretching temperature, stretch ratio, cooling temperature, heat treatment temperature and moisture content of the unstretched film were changed to those shown in the Table 1. In Comparative Example 1, the stretching temperature is lower than that of the method of the present invention, and the cooling procedure is not performed. In the example Comparative 2, the heat treatment temperature is lower than that of the method of the present invention. In the Comparative Example 3, the cooling procedure is not performed.

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Example 5

A laminate film was obtained stratifying the biaxially stretched EVOH film obtained in Example 1 and a low density polyethylene film that has a thickness of 40 µm per dry stratification, and further stratifying a stretched polypropylene film which has a thickness of 20 µm such that the film of polypropylene was in contact with the EVOH film by dry stratification. This stratified film was cut to 10 cm x 20 cm and folded in two with the low poly layer density inside to make a square. The ends and both side portions of the film folded in two were sealed thermally to produce an airtight bag. This bag was left to room temperature for 5 hours. It was not visually recognizable an undulation in the form of S.

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Comparative Example 4

A stratified film of the same way as in Example 5, using the biaxially film stretched obtained in Comparative Example 1. A bag was produced in the same way as in Example 5 using this movie stratified, and left, and then a ripple occurred in S. shape

As shown in Table 1, the film biaxially stretched obtained by the present invention has a small value for both the curvature coefficient and the Dry thermal shrinkage coefficient. Stratified produced by the use of such a film has no undulation in the form of S. In addition, the laminate looks good, and it looks like A satisfactory bag resulted. Moreover, the movie of stratified from Comparative Example 4 has a ripple in S shape, does not look good, and can result in a poor bag

The embodiments described in this application are they should consider for all purposes as illustrative and not limiting The scope of the invention is indicated by the attached claims.

Claims (8)

1. A method to produce a movie biaxially stretched comprising: stretch a movie made primarily of a ethylene-vinyl alcohol copolymer having a ethylene content of 15 to 70 mol% and a degree of saponification of 80 mol% or more, under heating, cool the film, and subject the cooled film to a treatment thermal, in which the heating temperature during stretching is 60 to 160 ° C, the temperature of cooling is a temperature of 30 to 100 ° C lower than the heating temperature during stretching, and the temperature for heat treatment is 150 to 190 ° C. 2. The method of claim 1, wherein Stretching is simultaneous biaxial stretching. 3. The method of claim 1 or 2, in the that the preheating takes place from 60 to 160ºC before stretching. 4. The method of any one of the claims 1 to 3, wherein a stretch ratio in a longitudinal direction is 2.5 to 4.5, a ratio of stretching in a transverse direction is 2.5 to 4.5, and a Stretch area ratio is 7 to 15 in the movie Biaxially stretched. 5. The method of any one of the claims 1 to 4, wherein the coefficient of curvature of the Biaxially stretched film is 15% or less. 6. A biaxially stretched film of ethylene-vinyl alcohol copolymer produced by the method of any one of claims 1 to 5, in the that the film has a dry thermal shrinkage coefficient in a longitudinal direction of 4.0% or less, and the coefficient of film curvature is 15% or less, in which the coefficient Dry thermal shrinkage of the film is calculated with with respect to the film that had been heat treated dry to 140 ° C for one hour. 7. A laminate comprising a layer made of the biaxially stretched copolymer film of ethylene vinyl alcohol of claim 6 and a layer made of another thermoplastic resin. 8. The laminate of claim 7, in The thermoplastic resin is a polyolefin.